Pieces of concrete falling from concrete structures have become a problem in recent years. This includes, for example, concrete falling from tunnels, expressway overpasses, railroad piers and bridges. The falling of concrete pieces refers to partial separation of the surface of concrete from the main structure due to some cause of deterioration, or detachment of the concrete in the form of a concrete piece as a result of the separation progressing. Various factors have been indicated as the cause of falling concrete, examples of which include those thought to be based on initial defects such as cracks formed at the time of construction or cold joints, those thought to be caused by damage such as cracking and separation caused by a shock such as an earthquake, and those thought to be attributable to deterioration caused by neutralization, salt damage or reaction with alkaline aggregate following construction of a concrete structure. In addition, there is also the problem of falling tiles caused by such factors as deterioration over time in structures such as building in which tiles are attached to an exterior wall.
In order to prevent concrete pieces falling from these concrete structures, in many cases a reinforcing layer is formed that is obtained by affixing a cloth containing fibers such as glass fibers or carbon fibers to the surface of a concrete structure with an adhesive, and applying an epoxy resin and so forth thereon to embed the fiber sheet in the resin. However, these methods have a large number of processes and make it difficult to shorten construction time and reduce costs. In addition, since considerable time can be required to acclimate and affix the sheet to the surface of the concrete structure, work efficiency is poor and can require considerable skill and expertise. Moreover, since a long period of time can be required for the adhesive to harden, it is difficult to shorten construction time, thereby having a considerable effect on construction. This method has these problems (see Japanese Unexamined Patent Application, First Publication No. H9-59937).
In addition, a method has been developed in recent years that prevents concrete pieces from falling without using a reinforcing agent. This is a spray method in which a protective material containing a rapid-curing urethane resin or urea resin is sprayed using a special apparatus, and forms an extremely hard resin film on the surface of a concrete structure in a short period of time. However, this method has problems such as requiring the use of a special spraying apparatus and the dispersal of the protective material into surrounding areas at the time of spraying.
Moreover, since the various reinforcing materials and protective materials used to prevent accidents caused by detachment of concrete pieces are opaque, there are problems such as difficulty in visually examining deterioration and cracking of concrete during post-construction maintenance, additional requirements in terms of time and labor, and the lack of an aesthetically pleasing appearance (see Japanese Unexamined Patent Application, First Publication No. 2005-213844 and Japanese Unexamined Patent Application, First Publication No. 2006-1812).
In addition, when preventing tiles from falling from structures such as buildings in which tiles are affixed to an exterior wall, the use of the method for preventing accidents caused by detachment of concrete pieces as previously described results in the problem of the appearance of the resulting tiled wall being different from the existing tiled wall.